It is well established that substance abuse treatment in the criminal justice system is effective at reducing drug use and related criminal behavior. Although drug and alcohol treatment are common mandates in criminal justice programs, only a minority of clients actually initiate treatment. This application will compare two intervention formats that target motivation to initiate and engage in substance abuse treatment among a group of probationers who have drug or alcohol treatment conditions. Six hundred drug and alcohol offenders in two probation sites (Baltimore, Maryland, and Dallas, Texas) will be randomized to receive: 1) an in-person motivational interviewing session (MI), 2) a motivational computer program (MC), or 3) intake and monitoring supervision as usual (SAU). The MI condition will be structured along the lines of the promising Check-Up format, which consists of an assessment and personalized feedback delivered in an MI style; the content of the MC condition will be drawn from previous literature on effective motivational computer programs. In addition, because of the much higher rates of infectious disease among criminal justice populations and the link between drug use and infectious disease, the MI and MC conditions would include a referral to HIV/AIDS testing and treatment for those participants who qualify. Both interventions will be delivered at the start of the probation process, with follow-up assessments at one, six, and twelve months. Primary outcomes include engagement and participation in substance abuse treatment; secondary outcomes include drug and alcohol use, probation progress, HIV testing and treatment, and criminal behavior. This project will be the first to develop and test two interventions for encouraging criminal justice clients to follow through with treatment recommendations, with the goal of increasing treatment initiation and reducing subsequent drug use and related risky behavior. It also contributes to ongoing partnerships with two large probation agencies -- the Dallas County Supervision and Corrections Department and the Maryland Division of Parole and Probation.